Grinding machines utilizing powered endless grinding belts are well known in the art. However, the workholders in such prior art grinding machines are generally movable in a single generally linear path relative to a powered grinding belt, and are not indexable or rotatable about an axis of the workholder. This results in generally non-uniform belt wear for the grinding belt mechanism, and oftentimes non-uniform ground surfaces on the workpieces being processed by the machine. By providing a feature of selective indexing of a workholder relative to the abrasive grinding belt, flatter ground surfaces on the workpieces may be provided, together with a breaking up of the grinding scratch pattern on the workpieces, and redistribution of the unit area grinding pressure. This is particularly true of workpieces mounted on the workholder which have generally non-uniform surface areas to be ground.